Method of cold rolling ferrous strip stock



- arnon on COLD ROLLING FERROUS srmr STOCK Walter R. Cavanagh, Detroit,and Robert C. Gibson, Birmingham, Mich., assignors to Parker Rust ProofCompany, Detroit, Mich., a corporation of Michigan No Drawing.Application January 25, 1956 Serial No. 561,354

Claims. (Cl. 1486 .15)

This invention concerns the art of cold rolling ferrous strip stockcontinuously. The invention specificallyrelates to an improvement in thecold rolling process which enables easier production of cold rolledstrip of superior flatness, smoothness and surface finish in comparisonto heretofore known cold rolled strip. The present improve mentcomprises a special processing of the strip after acid pickling andprior to cold rolling to facilitate the cold rolling operation.

It was early suggested in US. Patent No. 2,105,015 that the deformationof metal was facilitated by providing a phosphate coating on the metalsurface prior to the deforming operation. It has also been suggestedthat the drawing of wire, bar stock, tubes and the like is made easierby phosphate coating the part to be drawn. To the best of our knowledgethere has been no proposal of a process suitable for use in thecontinuous cold rolling of steel strip stock.

Present day cold rolling processing of steel strip stock comprisespreparing the strip surface for cold rolling and then cold rolling in areversing mill or a multiple stand mill. Low carbon steel, silicon steelor other steel strip, which emerges from a conventional hot rolling millusually has some residual rolling scale and corrosion products on itssurface. The preparation. for cold rolling normally includes processingthe hot rolled strip to clean the surface by passing it through a pickleline of conventional form which may, for example, include in sequenceone or more mineral acid dip stations, one or more water rinse stationsand an oiling station. In certain instances where the scale is heavy,the pickleline may include mechanical abrading stations or alkalistations prior to the acid dip stations. The steel strip is continuouslypassed through these sequential stages and is recoiled after oiling toawait the cold rolling operation. The rolling mill, whether reversing ormultiple stand, operates at speeds and under conditions which make itimpossible to feed directly from the pickle line to the rolling line.Because of this necessary but variable length delay between the picklingof the strip and its rolling, the corroding of the pickled strip becomesan important problem. It is for this reason that most pickle linesinclude a final oiling station. The oiling step is highly undesirablefrom the dual standpoints that it drips. from the pickled coils, makesthe working area slick, dirty and unsafe for workmen and that after coldrolling when the cold rolled strip is annealed the oil residue producesa surface coating of undesirable smut. It is one of the objects of thisinvention to provide a process which eliminates the necessity foroiling.

In order to facilitate the cold rolling of steel strip,

processing changes which are made must be adapted to current processesand,-of course, must avoid the introduction of complications. It isdesirable to improve the flatness of cold rolled strip stock, to providesmoother and cleaner cold rolled surfaces on strip stock but theseobjectives would not be worthy of attainment at appreciably greater costor at the expense of production United States Patent O 2,884,351Patented Apr. 28, 1959 the operator attempts continuously to adjust theroll'spacing to produce a rolled strip having uniform gauge but it willbe appreciated that at such speeds accuracy of gauge is subject to thehuman error which results from the time required to sense the necessityfor roll adjustment and then making it. The present invention provides aphosphate coating on the ferrous strip prior to cold rolling. It wasfound that when variations in the weight or thickness of the phosphatecoating on the surface of the strip exist, greater difficulty inmaintaining gauge is experienced by the operator. If the phosphatecoating weight varies widelyfrom point to point along the strip,attempts by the operator to correct for these variations sometimes causeside slipping and even ripping and tearing of the strip. Assume aportion of the strip of, say, 50 feet in length is coated with a heavierand thicker phosphate coating than the adjacent portions and is beingcold rolled in a conventional reversing rolling mill. As the thickportion begins to pass between the rolls, the operator senses diflicultyin holding gauge and applies pressure to force the rolls closer andattain gauge, but as the thick portion of the strip passes through therolls the extra applied pressure causes the roll to grab the followingportion of the strip and thus cause ripping or tearing. It is thereforethe most important object of this invention to provide means forcontinuously applying a substantially uniform phosphate coating to thesurfaces of ferrous strip to enable that strip to be continuously coldrolled.

It will be apparent that in order to produce sufficient pickled steelstrip to keep a cold rolling rnil'l in continuous production, the pickleline must necessarily operate continuously and at relatively rapidspeeds in order to be economic. Although actual speeds necessarily varyin difierent installations, pickle line speeds in the range of 150feet/minute to 450 feet per minute are common. One of the diflicultiesin supplying a process for continuously forming a phosphate coating onthe strip steel moving through a pickle line is to provide a solutionwhich will form the necessary coating in the limited time which isavailable for contact of the strip surface with the phosphate coatingsolution. For example, if the pickle line moves at feet per minute aphosphate coating tank having a 25 foot length provides only about 10seconds contact time for the strip. It will be apparent that as thepickle line speed increases, either the phosphate coating tank must begreatly lengthened or the coating solution must be adapted to act in amuch shorter time than 10 seconds, for example in 3 to 8 seconds. It isanother of the objects of the invention to provide processing ofsolutions which will provide the necessary coating in extremely shortperiods of time.

It was further found that in the conventional operation of a strip steelpickling line, delays in processing occur due to the necessity forstopping the line while the ends of coils are tacked together orsevered, and to the unexpected mechanical failures which sometimesoccur. During such stoppages, usually 2-10 minutes, but sometimes 30minutes, a portion of the strip is in contact with the phosphatesolution much longer than the normal time of 3-20 seconds, and it wasfound that during these stops that exposed portion of the strip receiveda heavier and thicker coating than the adjacent portions. This heavycoating would cause the difliculty in subsequent rolling mentionedhereinabove. It is thus another of the objects of this invention toprovide phosphate coating solutions which can produce a phosphatecoating on a moving fer- 3 rous strip stock-having a um weight of 5.0mgJsq. ft. in 10 seconds or less and a maximum weight of 200 mg./sq. ft.greater than the average weight achieved in 10 seconds on that strip.Another object is to supply means for providing a phosphate coating onmoving ferrous strip stock having a minimum weight of 50 mg./ sq. ft. ofsurface area and a maximum weight of 1000 mg./ sq. ft., but whichcoating does not vary more than 200 mg./ sq. ft. from the averagecoating weight which is prevalent on the surface of the strip.

Another object is to provide a phosphate coating which will enable theelimination of the use of a roughened surface roll such as a Pangbomroll in a reversing mill or in the last stand of a multiple stand milland yet produce a cold rolled sheet of suitable surface condition toprevent sticking on annealing.

Yet another object is to provide such a phosphate coating as to enablethe annealing of sheets, without sticking, of such cold rolled strip instacks that are higher than current practice and at temperatures up toabout 1750 F.; to provide such a phosphate coating as to enable thesubsequent stamping, in the hardened cold rolled condition of variousparts such as. electric motor laminations, which after assembly may beannealed without sticking at temperatures as high as about 1750 F.

One aspect of the present invention accomplishes the above and relatedobjects by providing certain phosphate coating solutions and certaincontrolled conditions for their use. In another aspect, this inventionprovides processing steps which accomplish the objectives of thisinvention by controlling the time and conditions of contact of the stripby the phosphate coating solution. It is also contemplated by thisinvention to introduce an additional step of preliminary treatment afterthe acid pickling and prior to the phosphate coating to enable theformation of the desired coating.

Broadly stated, the method of this invention comprises the provision ofaqueous acidic phosphate coating solutions which are capable ofproducing on the surface of a ferrous strip, normally pickled, a coatinghaving a minimum weight of 50 mg./sq. ft. of surface area in not morethan 10 seconds and a coating weight which does not vary more than 200mg./sq. ft. from the average coating weight deposited in 10 seconds, thecoating to have a maximum weight of 1000 mg. and preferably a maximum of500 m./sq. ft. A phosphate coating which does not vary more than 200mg./sq. ft. from the average coating weight on the surface of theferrous strip is, for the purposes of this description and the appendedclaims, considered to be a substantially uniform coating. .Whcn asubstantially uniform phosphate coating is present on the ferrous strip,that strip is capable of being continuously cold rolled in asatisfactory manner.

We have found that such coatings can be produced from aqueous acidiczinc phosphate coating solutions of certain composition when used undercertain controlled conditions. Due to the extremely short contact timewhich is available we have found that aqueous acidic manganese phosphatesolutions are unsatisfactory. We have also found thatalkali metalphosphate solutions such as aqueous acidic sodium or ammonium dihydrogenphosphates containing a chlorate accelerator, while producingapproximately the minimum coating weight which is desirable in 10seconds do not produce a coating which gives appreciable improvement inthe cold rolling operation. We have found that aqueous acidic zincphosphate solutions containing zinc in an amount in a range of 0.05% to1.5% and 0.4% to about 2.5% P and any of the conventional oxidizingagents known to be useable with such solutions, except chlorate, aresuitable for this purpose when the contact time between the ferrousstrip and the solution does not exceed 20 seconds. The proportion ofoxidizing agent which should be present in order to achieve the minimumcoating weight of 50 mg.'/ sq. ft. in seconds should fall within limitsset forth bequinones, etc.

low in detail. Such solutions when operated at conventional strengths ofbetween about 10 and 70 points and at conventional coating temperaturesranging from approximately 100'- F. to l F. depending upon theparticular zinc concentration and oxidizing agent-being employed willproduce the desired substantially uniform coating. The points of totalacid refers to the number of ml. of 0.1 N NaOH required to neutralize a10 ml. sample of the solution to a phenolphthalein endpoint. Thesolutions may opttionally contain the calicum ion in an amount in therange of about 0.012% to about 7.5% by weight. The presence of calciumin the coating solution apparently causes the production of somewhatfiner grain coatings and these coatings have been found to give themaximum assistance in the rolling operation, i.e., in reducing the rollpressure required, the power required, and in producing the smoothest,flattest strip having the best surface finish. For any particular actualconcentration of calcium and zinc the ratio of calcium to zinc should bebetween 1 calcium to 4 zinc and 5 calcium to l zinc, or a ratio ofcalcium to zinc from 0.25:5 and preferably in the range of 0.6:4.

As above indicated the solutions may contain conventional oxidizingagents such as nitrate, nitrite, hydrogen peroxide and organic nitrocompounds such as picric acid, m-nitrobenzene sulfonate anddinitrobenzene sulfonate, or bromates, iodates, t-butyl hydroperoxide,Nitrate and nitrite are the most desirable oxidizing agents for thepurposes of this invention. When nitrate is employed,- the ratio ofnitrate to phosphate, N0,:P0 may satisfacto 'y extend from 0.5 :5.0.When nitrite is employed the ratio of NO,:P0 may satisfactorily extendfrom about 0.001 to about 0.05; for m-nitrobenzene sulfonate the ratiomay extend from about 0.15 to about 3.0; for hydrogen peroxide the ratiomay extend from about 0.002-0.0l and for dinitrobenzene sulfonate theratio may extend from about 0.1-1.5. When the other more infrequentlyemployed oxidizing agents such as bromates, methylene blue, iodates,picric acid, t-butyl hydro-peroxide, sulfites, hypochlorites,periodates, nitroguanidine, nitromethane, nitrourethane, nitraniline,nitrophenol, quinones, etc. are used, they may be used in quantitieswhich produce an effect on the rate of coating formation which isequivalent to that produced by the above specified range for nitrate. Itis also satisfactory to employ a mixture of oxidizing agents, if desiredwith the appropriate quantity of the mixture being that quantity whichproduces an efiect on the rate of the coating formation which is equalto the effect obtained from the use of nitrate in the quantities abovestated.

The phosphate coating of this invention, after convenonsl cold waterrinsing, is beneficial in avoiding corrosion on the strip during thedelay period prior to rolling and completely eliminates the need for theconventional oiling step. In certain instances, however, where theconditions which cause corrosion are worse than usual, it may bedesirable and this invention contemplates the rinsing of the phosphatecoated surface in an additional corrosion rinse such as a dilute aqueoussolution of chromic acid, borax, sodium nitrite, soda ash, etc., in aconventional manner.

In its final aspect it has been found that the objects of this inventionmay be realized by adding a pretreatment step in the process followingthe acid pickling step and prior to the introduction of the strip intothe phosphate coating solution. It has been found that by contacting thepickled strip with certain aqueous pretreatment solutions which arecapable of activating the surface to make it more receptive to attack byacidic phosphate treating solutions, it is possible to greatly increasethe initial coating producing capacity of zinc phosphate solutions onsuch surfaces so that the most desired coating weight may be obtained inthe extremely limited treatment time which is available, for example,3-8 seconds. It has been found to be satisfactory to employ as such apretreatment soluoils,

lion aqueous acidic solution of oxalic acid, an aqueous solution ofdisodium phosphate or tetra sodium pyrophosphate containing a smallamount of titanium (e.g. up to 0.05% Ti) as a compound or zirconium as acompound; an aqueous solution of tetra sodium pyrophosphate; a mixtureof tetra sodium pyrophosphate and meta phosphates in aqueous solution; adialkali metal phosphate containing up to 0.05% of lead, tin or arsenic;and a mixture of tetrasodium pyrophosphate with disodium phosphatecontaining a small amount of a titanium or zircomum compound. Examplesof suitable titanium compounds for this purpose are titanium chloride,titanium hydroxide, titanium nitride and titanium potassium oxalate.

The desired coating weight of a substantially uniform phosphate coatingcan also be obtained by regulating the time of contact between theferrous strip and the coating solution irrespective of theuncontrollable shutdowns or stoppages which may occur in the normaloperation of the pickling line. This invention contemplates theprovisionof mechanical means for removing the strip stock from the phosphatecoating solution substantially simultaneously with any stoppage of thestrip and immediately water rinsing the removed strip to free thesurface of active phosphate coating solution. Various mechanical meansfor accomplishing this purpose will be apparent to those skilled in theart. One example of such a means may comprise roller means at theentering end of the phosphate coating tank and roller means at the exitend of the tank so adjusted as to cause the ferrous strip to be immersedwell down into the phosphate coating solution during normal travel ofthe strip. The rolls may be suitably mounted on vertically moveableelements which are actuated to raise those rolls substantiallysimultaneously with the stoppage of horizontal motion of the strip so asto remove the strip from the solution. Water spray means mounted so asto be positioned above and below the strip, move into position after thestrip has been raised item the solution to spray the surfaces and rinsethe phosphate coating solution therefrom. The present inventioncontemplates the application of the phosphate coatiug solution byspraying as well as by immersion. When the coating solution is beingapplied by spraying, conventional electrical interlocks may be providedwhich automatically shut off the spray upon strip stoppage and start theapplication of a water rinse from the spray or separate spray nozzles.

The cold rolling can be done on a reversing or multiple stand mill byemploying conventionally used lubricants during the rolling operation.Any of a number of satisfactory lubricants may be employed includingoils, such as mineral oil, palm oil, rape seed oil, etc. Lubricants forthis purpose are preferably used in aqueous form, either as a solutionor emulsion. Dilute aqueous solutions consisting of, for example, 1% to3% oil and the balance water, of a water soluble mineral oil, or a lardbase oil together with a conventional emulsifying agent for such havebeen satisfactorily employed. One specific aqueous base lubricant whichhas been used with unusual success is a mixture of lard oil and a fattyacid and has the following analysis: Fatty acid (calculated as oleicacid), l2.9% by weight, iodine number 36.9 and a saponification numberof 32.4. A small amount of an emulsifying agent to make this mixed oilwater soluble is added to a solution containing 1%2% of this mixed oil,balance water.

The below given examples illustrate in greater detail the method of thisinvention but it is to be understood that the particular proportions ofingredients therein set forth or the particular conditions of operationwhich are recited are not to be considered as the limits of theinvention but rather illustrative satisfactory operative conditionsonly.

Example I An aqueous acidic phosphate solution tank was installed as thelast station in a strip steel sulfuric acid pickling line whichcomprised a sulfuric acid pickling station, a water rinse station andthe phosphate crating solution station. An aqueous acidic zinc phosphatesolution was prepared in the phosphate solution and analyzed to containin percent w./v.: zinc 0.73, nitrate 2.07, PO 1.26, total acid 29.8,free acid 4.2. The number of free acid points refers to the number ofml. of 0.1 N NaOH required to neutralize a 10 ml. sample of the solutionto a brom phenol blue endpoint. The solution also contained 0.008% N0which was maintained at approximately that concentration during use. Thesolution showed freedom from the ferrous ion. The solution wasmaintained at a temperature of about 170 F.l F. and hot rolled lowcarbon steel strip was fedthrough the sulfuric acid pickle, water rinsedand thereafter introduced into the above solution and maintained incontact with the coating solution, measured times of 10 seconds, 20seconds, 30 seconds. Samples of the processed strip stock were checkedfor the weight of coating formed on the surface in these time periods.After 10 seconds it was found that the strip had a coating weight ofmg./sq. ft. of surface area, a weight of 275 mg./sq. ft. after 20seconds and 385 mg./sq. ft. after 30 seconds. The strip emerging fromthe phosphate coating solution was coiled in the conventional manner. insome cases the coils were immediately rolled on a reversing rolling milland in others a. time delay, measured in days, occurred before therolling was done. The strip was passed through the Bliss rolling machinea'plurality of passes and in most cases was reduced from about 0.1 inchto 0.068" in one pass, to 0.05" in two passes, to 0.038 in three passes,to 0.029" in four passes and to 0.025 in five passes. During the rollingthe strip and the rolls were continuously flooded with an aqueous baselubricant of the type disclosed above in detail. During the rolling ofthese coils, no difficulty was experienced with the portions whichreceived coating having less than 275 mgJsq. ft. coating weight whichcorresponds to the weight received after 20 seconds of treatment. Somedifiiculty was encountered, however, when portions of the stripcorresponding to phosphate coating treatment times exceeding 20 secondspassed between the rolls. This difliculty consisted of trouble inmaintaining the desired gauge and when an extra heavy coating weightcorresponding to approximately 10 minutes contact time with thephosphate coating solution (about 1000 mg./sq. ft.) passed between therolls, the stripwas actually severed due to grabbing of the portion ofthe strip which followed the extra heavy coating weight portion. Aninspection of the cold rolled stock showed the same to be flat,relatively free of surface defects and unusually clean in appearance.There did appear to be, however, some residual phosphate coating on thesurface and this was evidenced by the fact that stacked sheets takenfromthese coils were annealed in 50" heights in a dioxidizing atmosphere at1275 F. without sticking. Normally, sticking is encountered at thattemperature when the stack is higher than about 36". Portions of thisstrip were painted in the as rolled condition and checked for salt sprayand corrosion resistance. The results indicated some improvement in saltspray and corrosion resistance in comparison to bare metal, but thebenefit was not as great as that received from phosphate treatmentsapplied specifically for paint receptivity only.

Other solution compositions which, when operated in the pickling lineunder conditions substantially similar to those described in Example Iare operative to form a substantially uniform coating suitable for thepurposes of this invention are given in the examples below.

Example 11 An aqueous acidic solution was prepared and upon analysisfound to contain in percent w./v.: zinc 0.29,

7 nitrate 1.21, PO 0.92, iron 0.20, total acid 21.1 and free acid 3.2.

Example III An aqueous acidic solution was prepared and upon analysisfound to contain in percent w./v.: zinc 0.19, nitrate 0.30, PO 1.38,iron 0, nitrite 0.006, calcium 0.14, free acid 1.5 and total acid 15.6.

Example V An aqueous acidic solution was prepared and upon analysisfound to contain in percent w./v.: zinc 0.35, nitrate 1.55, nitrite0.006, P 0.84, iron 0, calcium 0.34, total acid 20.2 and free acid 2.7.

Example VI An aqueous acidic solution was prepared and upon analysisfound to contain in percent w./v.: zinc 0.21, nitrate 2.17, PO, 0.64,iron 0, calcium 0.53, nitrite 0.004, total acid 15.1, free acid 1.8.

Example VIII An aqueous acidic solution suitable for operation attemperatures between about 110 F. and 135 F. by spraying was preparedand analyzed to contain in percent w./v.: zinc 0.11, nitrate 0.64, P00.76, iron 0, nitrite 0.006, total acid 10.6, free acid 0.5.

Example IX An aqueous acidic solution was prepared and analyzed tocontain in percent w./v.: zinc 0.12, PO, 0.46, iron 0, hydrogen peroxide0.012, total acid 6.9 and free acid 0.4.

Example X A tank was prepared to contain a 2% solution of oxalic acid inwater. Hot rolled low carbon steel strip was fed through the sulfuricacid pickle line described in Example I, water rinsed and then fed intothe oxalic acid solution maintained at room temperature so that thesurface was in contact with the strip for thirty seconds. The strip wasthen rinsed for one minute in hot water and then processed directly intothe phosphate coating solution of Example I. Portions of the stripcorresponding to times of contact with the phosphate coating solution ofseconds, seconds and 30 seconds were removed and analyzed for coatingweight. After 10 seconds the coating weight was found to be 285 mg./sq.ft. of surface area, after 20 seconds 330 mg./sq. ft., and after 30seconds 450 mg./sq. ft. It will be noticed that this additionaltreatment approximately doubled the coating weight which was obtainedafter 10 seconds contact with the solution of Example I and that thesubsequent increase in coating weight was relatively smaller than in theabsence of the additional treatment. Satisfactory rollingcharacteristics were obtained upon rolling the coils coming from tlisprocessing when the rolling was done under conditions which weresubstantially the same as those described in Example I.

Example XI In a manner comparable to that set forth in Example X,another treatment solution consisting of a 1% solution of disodiumphosphate in water and containing a small amount (between 0.005% and0.05% Ti) of a titanium compound, believed to be titanium chloride, wasprepared. Hot rolled low carbon steel strip which had been 8preliminarily sulfuric acid pickled was immersed in this solution,maintained at 190 degrees for thirty seconds, removed from this solutionand fed directly mto the phosphate coated solution of Example I. Samplesofthe strip representing phosphate coating solution contact times of 10seconds, 20 seconds and 30 seconds were removed from the coil andanalyzed for coating'weight. After 10 seconds the coating weight wasfound to 300 mg./sq. ft., 500 mg./sq. ft. after 20 seconds and 620mg./sq. ft. after 30 seconds.

Example XII Another intermediate treatment solution was prepared andused in a manner similar to that set forth in Example X. The solutionwas built up to contain in percent w./v. 0.87% tetra sodiumpyrophosphate and 0.13% of disodium phosphate containing titanium (asdescribed in Example XI). Withthe solution maintained at 160 F., theship was contacted for one minute, hot water rinsed for one minute andthen passed into the phosphate coating solution of Example I. In similarmanner samples of the coils were analyzed for coating weights. After 10seconds the coating weight was found to be 360 mg./sq. ft., 410 mg./sq.ft. after 20 seconds and 440 mg./sq. ft. after 30 seconds.

What is claimed is:

1. A method for treating continuous ferrous strip stock which comprisesthe steps of pickling the strip, contacting the said pickled strip whilethe same is moving with an aqueous acidic zinc phosphate coatingsolution comprising as the essential coating producing ingredients zincin an amount in the range of 0.05 1.5% by weight, 0.4 to about 2.5% P0and an oxidizing agent other than chlorate in an amount suflicient toproduce a coating weight of at least 50 mg. per square foot in not morethan 10 seconds, and regulating the time of contact of said pickledstrip with said solution so as to produce a coating which has a weightin the range of about 50 mg./ sq. ft. to about 1000 mg./sq. ft. andwhich varies frmn the average coating weight prevalent on said strip bynot more than about 200 mg./sq. ft.

2. A method for treating ferrous strip stock which comprises the stepsof pickling the strip, contacting the pickled strip with an aqueousacidic zinc phosphate coating solution comprising as the essentialcoating producing ingredients zinc in an amount in the range of 0.05%-1.5% by weight, 0.4 to about 2.5 P0 and an oxidizing agent other thanchlorate in an amount sutficient to produce a coating weight of at least50 mg. per square foot in not more than 10 seconds, controlling the timewhich said strip is in contact with said solution to not more than 20seconds to thereby produce a coating which varies from the averagecoating weight prevalent on said strip by not more than about 200mg./sq. ft., and thereafter continuously cold rolling said strip stock.

3. In a method for treating continuous ferrous strip stock whichcomprises the steps of pickling the strip, contacting-the said pickledstrip while the same is moving with an aqueous acidic zinc phosphatecoating solution comprising as the essential coating producingingredients zinc in an amount in the range of 0.05%-1.5% by weight, 0.4to about 2.5% P0 calcium in an amount in the range of about 0.12% toabout 7.5% by weight and an oxidizing agent other than chlorate in anamount suflicient to produce a coating weight of at least 50 mg. persquare foot in not more than 10 seconds, and regulating the time ofcontact of said pickled strip with said 0.4 to about 2.5% P calcium inan amount in the range of about 0.12% to about 7.5% by weight, and anoxidizing agent selected from the group consisting of nitrate, nitrite,hydrogen peroxide, m-nitrobenzene sulfonate, dinitrobenzene sulfonate,bromate, iodate, t-butyl hydroperoxide, quinone, hypochlorite, periodatesulfite, methylene blue, nitroguanidine, nitromethane, nitrourethane,nitraniline and nitrophenol in an amount having an effect on the rate ofcoating equivalent to 2% to 12% nitrate, and regulating theconcentration of said oxidizing agent in said solution and the time ofcontact of said strip with said solution so as to produce a coatinghaving a minimum weight of 50 mg./sq. ft. and which is substantiallyuniform.

5. A method for treating continuous ferrous strip stock which comprisesthe steps of pickling the strip, contactin 'the pickled strip wtih anaqueous solution capable of activating the surface to render it morereceptive to the formation of a phosphate coating, contacting said stripwith an aqueous acidic zinc phosphate coating solution comprising as theessential coating producing ingredients zinc in an amount in the rangeof 0.05%- 1.5% by weight, 0.4 to about 2.5% P0 and an oxidizing agentother than chlorate in an amount sufiicient to produce a coating weightof at least 50 mg./sq. ft. in not more than 10 seconds, and regulatingthe concentration of said oxidizing agent in said solution and the timeof contact of said strip with said solution so as to produce a coatingwhich has a weight in the range of about 50 mg./sq. ft. to about 1000ling/sq. ft and which varies from the average coating weight prevalenton said strip by not more than about 200 mg./sq. ft.

6. A method for treating continuous ferrous strip stock which comprisesthe steps of pickling the strip, contacting the pickled strip with anaqueous acidic zinc phosphate coating solution comprising as theessential coating producing ingredients zinc in an amount in the rangeof 0.05%-1.5% by weight, 0.4 to about 2.5% P0 and an oxidizing agentother than chlorate in an amount sufficient to produce a coating weightof at least 50 mg. per square foot in not more than 10 seconds,controlling the time which said strip is in contact with said solutionto not more thm 20 seconds to thereby produce a coating which variesfrom the average coating weight prevalent on said strip by not more thanabout 200 mg./ sq. ft., continuously cold rolling said strip stock, andthereafter annealing said strip stock.

7. A method as claimed in claim 4 wherein the ratio of calcium to zincis between 0.6 to 4.0.

8. A method as claimed in claim 4 wherein the oxidizing agent is nitrateand the ratio of calcium to zinc is 0.6 to 4.0.

9. The method as claimed in claim 4 wherein the oxidizing agent isnitrite and the ratio of calcium to zinc is between 0.6 to 4.0.

10. A method for treating continuous ferrous strip stock which comprisesthe steps of pickling the strip, contacting the said pickled strip whilethe same is moving with an aqueous acidic'zinc phosphate coatingsolution comprising as the essential coating producing ingredients zincin an amount in the range of 0.05% to 1.5% by weight, 0.4% to about 2.5P0 and an oxidizing agent other than chlorate in an amount suflicient toproduce a coating weight of at .least mg./sq. ft. in not more than 10seconds, so as to produce a coating having a weight in the range ofabout 50 mg./sq. ft. to about 1000 mg./sq. ft. and varying from theaverage coating weight prevalent on said strip by not more than about200 mg./ sq. ft., continuously cold rolling said strip stock andthereafter annealing said strip stock.

References Cited in the file of this patent UNITED STATES PATENTS1,279,101 Gravell Sept. 17, 1918 2,105,015 Singer Jan. 11, 19382,164,042 Ronig June 27, 1939 2,230,319 Canzler Feb. 4, 1941 2,293,716Darsey Aug. 25, 1942 2,298,312 Romig Oct. 13, 1942 2,314,887 Lodeesen etal Mar. 30, 1943 2,351,605 Gibson June 20, 1944 2,462,196 Jernstedt Feb.22, 1949 2,476,345 Zavarella July 19, 1949 2,479,564 Gilbert Aug. 23,1949 7 2,516,008 Lum July 18, 1950 2,522,176 Holden Sept. 12, 19502,540,314 Amundsen Feb. 6, 1951 2,608,496 Tuttle et a1. Aug. 26, 1952

1. A METHOD FOR TREATING CONTINUOUS FERROUS STRIP STOCK WHICH COMPRISESTHE STEPS OF PICKLING THE STRIP, CONTACTING THE SAID PICKLED STRIP WHILETHE SAME IS MOVING WITH AN AQUEOUS ACIDIC ZINC PHOSPHATE COATINGSOLUTION COMPRISING AS THE ESSENTIAL COATING PRODUCING INGREDIENTS ZINCIN AN AMOUNT IN THE RANGE OF 0.05%-1.5% BY WEIGHT, 0.4 TO ABOUT 2.5% PO4AND AN OXIDIZING AGENT OTHER THAN CHLORATE IN AN AMOUNT SUFFICIENT TOPRODUCE A COATING WEIGHT OF AT LEAST 50 MG. PER SQUARE FOOT IN NOT MORETHAN 10 SECONDS, AND REGULATING THE TIME OF CONTACT OF SAID PICKLEDSTRIP WITH SAID SOLUTION SO AS TO PRODUCE A COATING WHICH HAS A WEIGHTIN THE RANGE OF ABOUT 50 MG./ SQ. FT TO ABOUT 1000 MG./SQ.FT. AND WHICHVARIES FROM THE AVERAGE COATING WEIGHT PREVALENT ON SAID STRIP BY NOTMORE THAN ABOUT 200 MG./SQ.FT.